I think you're right.
You can certainly increase the odds of finding a good prospect by scouting high on your list.
However, you will probably find some good prospects by scouting low, but there is more probability for those good prospects to be ranked higher on other managers lists rather than lower, so you don't increase you're chances of them not being drafted.
The only way to increase your chances of getting a good prospect, aside from tanking, is spending more on scouting.
"Air is beautiful, yet you cannot see it. It's soft, yet you cannot touch it. Air is a little like my brain." - Jean-Claude Van Damme